William Bengen: The 5% Rule for Retirement Spending (EP.135)

Episode Summary

Executive Summary: Bill Bengen, the originator of the 4% withdrawal rule, discusses how his research evolved from a simple historical framework into a more nuanced, regime-based approach incorporating CAPE and inflation. He argues current conditions may allow higher withdrawals than many advisors assume, stresses low costs and diversification, and shares practical retirement-planning techniques, including graphing portfolios against historical templates.

Main Topics: Origins and meaning of the 4% rule (Priority: 5/5): Bengen explains his 1994 finding: a retiree drawing from a tax-deferred portfolio could withdraw 4% in year one, then adjust for inflation, and historically avoid running out of money over 30 years using a 50/50 stock-bond allocation. Evolution to 4.5% and beyond (Priority: 5/5): He later added small-cap stocks, which improved diversification and return, lifting the sustainable withdrawal rate to about 4.5%. He also notes that with more asset classes, some studies suggest even higher rates may be feasible. 2020 research on CAPE and inflation regimes (Priority: 5/5): Bengen highlights that withdrawal rates depend not just on valuation but also on inflation. High CAPE does not necessarily imply very low safe withdrawal rates if inflation is low, and he suggests current conditions may support rates above 4.5%. Practical retirement-income management (Priority: 4/5): As a practitioner, Bengen focused on helping clients set lifestyles they could sustain, monitoring portfolio progress annually, and using historical templates to compare real retirements against analogous past scenarios. Portfolio design, fees, and bonds (Priority: 4/5): He emphasizes low-cost, index-like funds and warns that high fees reduce sustainable withdrawals. He also questions the usefulness of bonds in today’s low-rate environment, though he notes they helped in prior decades. Behavioral constraints on allocation and spending (Priority: 4/5): Bengen argues that while small-cap stocks can maximize safe withdrawal rates in historical data, their volatility makes them hard for clients and advisors to tolerate. He also supports stable retirement lifestyles over highly dynamic spending rules. Career path and definition of success (Priority: 3/5): He recounts moving from aerospace engineering and the family bottling business into financial planning, then research. He defines success as learning or creating something, helping someone, and appreciating the mystery of life.

Key Arguments: The original 4% rule was based on U.S. historical data, a 30-year horizon, and a 50/50 large-cap stocks and intermediate-term Treasuries portfolio. The impact of the 4% rule came from offering a simple, evidence-based alternative to the wide range of unsupported withdrawal-rate guesses used in practice. Adding small-cap stocks improved diversification and raised the historically sustainable withdrawal rate from roughly 4.0%-4.2% to about 4.5%. Withdrawal rates should be evaluated by both valuation and inflation regime; high valuations alone do not always imply low sustainable withdrawals. Inflation is more dangerous than market declines because inflation permanently raises required withdrawals, while market losses can eventually recover. For U.S. investors, high withdrawal rates may be possible in favorable regimes; Bengen cites past periods where 6.5%-7% or even higher would have worked. Low-cost investing matters because fees directly reduce net portfolio returns and therefore lower sustainable withdrawal rates. Retirees should focus on what they can control—spending and behavior—rather than relying on risky assumptions about higher investment returns. Small-cap-only strategies can look excellent in historical simulations, but real-world volatility and behavioral tolerance make them impractical for many retirees. A stable, maintainable lifestyle is often better than a highly dynamic spending rule, though some flexibility is sensible when conditions change. Bonds are not automatically “safe” in retirement; in low-rate environments they may add little diversification or income benefit and can drag on withdrawal rates. Historical withdrawal-rate research is U.S.-specific and may not generalize across countries because return and inflation histories differ. Historical-template tracking can help advisors judge whether a retiree is off-track and whether deviations are due to temporary market noise or a more serious inflation problem.

Data Points: Original withdrawal rate: 4% - Bengen’s 1994 paper on a 30-year retirement horizon using U.S. stocks and bonds Portfolio allocation: 50/50 - Optimal allocation in the original research using large-cap stocks and intermediate-term Treasuries Updated withdrawal rate: 4.5% - Later research incorporating small-cap stocks Higher possible withdrawal rates: 5% to 5.5% - Bengen’s view of what may be doable with a well-diversified portfolio in current conditions Worst-case historical investor: October 1968 retiree - Example used to illustrate the worst historical retirement sequence with low returns and high inflation Average historical withdrawal rate: 7% - Bengen says a random historical retiree could average about this rate Maximum historical withdrawal rate: 13% - Upper-end historical outcomes for lucky retirees in his analysis 40-year withdrawal rate: 4.2% - Bengen’s estimate for a longer retirement horizon than 30 years Inflation stress scenario: Double-digit inflation for 15 years - Scenario that broke the 4% rule and reduced it to about 3.8% Broken-rule withdrawal rate: 3.8% - Withdrawal rate under extreme prolonged inflation in Bengen’s stress test March 2009 withdrawal potential: 6.5% to 7% - Bengen’s example of favorable market conditions allowing higher withdrawals Small-cap stock annual extremes: -65% to +150% - Illustration of volatility in small-cap stocks Average withdrawal with 100% small-cap stocks: 13% - Historical average withdrawal rate in Bengen’s small-cap research One lucky small-cap investor: 25% - Best-case historical outcome cited for small-cap-only strategy Historical comparison countries: 23 countries - Reference to global safe-withdrawal-rate research using Dimson-Marsh-Staunton data Countries where 4% held: Canada, New Zealand, United States - Bengen referenced survivorship-bias concerns in cross-country data Low-end foreign withdrawal rate examples: 0.2% - Example of extremely low safe withdrawal rates in some countries such as Italy and Japan Career timing: Age 40 - Bengen began entering financial planning/research later in life after prior careers Family business scale: 7 million customers - Size of the soft drink bottling business his family ran in the New York metro area

Pivotal Quotes: "If you were withdrawing during retirement from a tax-deferred account and you expect to live for 30 years and you want any money to live for 30 years, a 4% withdrawal rate the first year and then increasing for inflation each year after that would has always worked historically." — William Bengen: Summarizing his 1994 research finding "I think they can be probably more optimistic unless we get into a situation where PEs go to 100 or inflation comes in a big way. Concerns me, inflation more than anything else." — William Bengen: Discussing current withdrawal-rate conditions and what could derail them "It doesn't make sense to take more risk in your investments to get a higher withdrawal rate. That's dangerous because there's no guarantees that'll happen." — William Bengen: Explaining his practice philosophy with retirees

Implications: Listeners should treat the 4% rule as a historical guide, not a law. Safe withdrawals depend heavily on valuation, inflation, costs, and behavior, so retirement plans should be flexible, low-cost, and periodically reviewed against realistic historical scenarios.